Multiplex data acquisition modes for ion mobility-mass spectrometry

ABSTRACT

A method and apparatus for multiplexed data acquisition for gas-phase ion mobility coupled with mass spectrometry is described. Ion packets are injected into an ion mobility drift chamber at a rate faster than the ion mobility separation arrival time distribution. The convoluted arrival time distributions thus generated are deconvoluted by a mass spectrometer and post-processing algorithms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional application Ser.No. 60/591,568, filed Jul. 27, 2004.

TECHNICAL FIELD

This invention describes a method for multiplexed data acquisition forgas-phase ion mobility coupled with mass spectrometry. Ion packets areinjected into an ion mobility drift chamber at a rate faster than theion mobility separation arrival time distribution. The convolutedarrival time distributions thus generated are deconvoluted by a massspectrometer and post-processing algorithms. Sensitivity and throughputcan be improved by factors of ca. 10 to 1000 by using the correlateddata acquisition modes of this invention and further improvements can begained by multiplexing ion mobility-mass spectrometry/mass spectrometrytechniques for nearly simultaneous parent and daughter ion analysis.

BACKGROUND OF THE INVENTION

Two-dimensional gas-phase separations based on ion mobility(IM)-time-of-flight mass spectrometry (TOFMS) have demonstrated uniquepotential in the analysis of a wide range of materials and more recentlyin the analysis of complex mixtures of biomolecules [T. Wyttenbach andM. T. Bowers, Gas-Phase Conformations: The Ion Mobility/IonChromatography Method, Top. Curr. Chem. 225, 207-232 (2003) andreferences therein; and C. S. Hoaglund-Hyzer, A. E. Counterman, and D.E. Clemmer, Anhydrous Protein Ions, Chem. Rev. 99, 3037-3079 (1999) andreferences therein.]

Gas-phase ion mobility (IM) provides ion separation by generating orinjecting ions (and gaseous neutral species) in/into a gas-filled drifttube (typically 1 to 760 Torr) where they migrate under the influence ofa weak electrostatic-field (typically 1 to 100 V cm⁻¹ Torr-1) and areimpeded by collisions with the background gas. Biologically relevantions are injected into the drift cell by using pulsed ion sources (e.g.,matrix assisted laser desorption/ionization (MALDI)) or by pulsing acontinuous ion source (e.g., electrospray (ESI) or ion spray). Othertechniques to generate biologically relevant ions (and gaseous neutralspecies) may be used, such as surface enhanced laserdesorption/ionization (SELDI). Other nonlimiting examples includeatmospheric pressure MALDI, ultraviolet MALDI, infrared MALDI, directLDI (laser desorption/ionization), nanospray, photoionization,multiphoton ionization, resonance ionization, thermal ionization,surface ionization, electric field ionization, chemical ionization,atmospheric pressure chemical ionization, radioactive ionization,discharge arc/spark ionization, laser induced breakdown ionization,inductively coupled plasma ionization, direct current plasma ionization,capacitively coupled plasma ionization, glow discharge ionization,microwave plasma ionization, and any combinations thereof. The theory ofIM is fully developed in texts by Mason and McDaniel [E. W. McDaniel andE. A. Mason, The Mobility and Diffusion of Ions in Gases, Wiley, NewYork, N.Y. (1973); E. A. Mason and E. W. McDaniel, Transport Propertiesof Ions in Gases, John Wiley & Sons, Inc., New York, N.Y. (1988)], andthe combination of IM with quadrupole mass spectrometry and subsequentlytime-of-flight mass spectrometry (TOFMS) dates back to the early 1960's[W. S. Barnes, D. W. Martin, and E. W. McDaniel, Mass SpectrographicIdentification of the Ion Observed in Hydrogen Mobility Experiments,Phys. Rev. Lett. 6, 110-111 (1961); K. B. McAfee Jr. and D. Edelson,Identification and Mobility of Ions in a Townsend Discharge byTime-Resolved Mass Spectrometry, Proc. Phys. Soc. London 81, 382-384(1963)]. The mobility (K) of an ion is determined by the ratio of thedrift velocity (v_(d)) to the electric field strength (E):

$\begin{matrix}{K = \frac{v_{d}}{E}} & \lbrack 1\rbrack\end{matrix}$

When the ion-neutral collision energy nears the thermal energy of thesystem, the mobility approaches the so-called “low-field” limit and canbe related to the collision cross-section (Ω), or apparent surface area,of the ion:

$\begin{matrix}{K = {\frac{3}{16}\frac{q}{N}\left( {\frac{1}{\mu}\frac{2\pi}{k_{B}T}} \right)^{\frac{1}{2}}\frac{1}{\Omega}}} & \lbrack 2\rbrack\end{matrix}$

Where N is the number density of the drift gas, q is the ion charge (inMS techniques this is typically termed ze), μ is the reduced mass of theion-neutral collision pair, k_(b) is Boltzmann's constant, and T is thetemperature of the system. Thus, IM provides separation selectivitybased on the charge-to-collision cross-section (q/Ω) ratio of theanalyte ion in a particular background drift gas, in contrast with MSbased ion separation, which separates analyte ions on the basis of theirmass-to-charge (m/z) ratio.

Analyte selectivity based on ion mobility separation provides severalimportant advantages over prior art solution-based purification (e.g.,high performance liquid chromatography) or gas-based mass-to-chargeselection (i.e., MS) of biological molecules: (i) in many cases isobaricand isoform species (e.g., structural and/or conformational isomers) canbe separated [F. W. Karasek and D. M. Kane, Plasma Chromatography ofIsomeric Halogenated Nitrobenzenes, Anal. Chem. 46, 780-782 (1974); J.C. Tou and G. U. Boggs, Determination of Sub Parts-Per-Million Levels ofSec-butyl Chloropiphenyl Oxides in Biological Tissues by PlasmaChromatography, Anal. Chem. 48, 1351-1357 (1976); T. W. Carr, PlasmaChromatography of Isomeric Dihalogenated Benzene, J. Chrom. Sci. 15,85-88 (1977); D. F. Hagen, Characterization of Isomeric Compounds by Gasand Plasma Chromatography, Anal. Chem. 51, 870-874 (1979)], (ii) theseparation mechanism does not rely on solution-phase physical properties(e.g., hydropathy, isoelectric point, affinity, etc.) [E. W. McDanieland E. A. Mason, The Mobility and Diffusion of Ions in Gases, Wiley, NewYork, N.Y. (1973); E. A. Mason and E. W. McDaniel, Transport Propertiesof Ions in Gases, John Wiley & Sons, Inc., New York, N.Y. (1988)], (iii)it is amenable to a wide variety of molecular classes or complexmixtures thereof (e.g., proteins, lipids, oligonucleotides,carbohydrates, etc.) [J. M. Koomen, B. T. Ruotolo, K. J. Gillig, J. A.McLean, D. H. Russell, M. Kang, K. R. Dunbar, K. Fuhrer, M. Gonin, andJ. A. Schultz, Oligonucleotide Analysis with MALDI-Ion Mobility-TOFMS,Anal. Bioanal. Chem. 373, 612-617 (2002)], and (iv) in many cases it issensitive and selective for post-translationally modified peptides (orproteins) [B. T. Ruotolo, G. F. Verbeck, L. M. Thompson, A. S. Woods, K.J. Gillig, and D. H. Russell, Distinguishing Between Phosphorylated andNonphosphorylated Peptides with Ion Mobility-Mass Spectrometry, J.Proteome Res. 1, 303-306 (2002)].

Contemporary IM and IM-MS is performed by injecting ions into the driftcell slower than the transient rate of ion separation necessary toretain analyte injection/detection time correlation (i.e., at a rate<t_(d) ⁻¹, where t_(d) is the drift time of the ions through themobility cell). Traditionally this is termed the “pulse-and-wait”approach. However, significant enhancements in signal-to-noise (S/N) andthroughput can be realized by adapting multiplex data acquisitionmethods to IM-MS. Fourier transform (FT), Hadamard transform (HT), andcorrelation techniques are commonly used in optical and molecularspectroscopy, but their application to mass spectrometry has, untilrecently, been limited to FT-ion cyclotron resonance-MS [M. Harwit andN. J. A. Sloane, Hadamard Transform Optics, Academic Press, New York,N.Y. (1979); A. G. Marshall, Ed., Fourier, Hadamard, and HilbertTransforms in Chemistry, Plenum Press, New York, N.Y. (1982); A. G.Marshall and F. R. Verdun, Fourier Transforms in NMR, Optical, and MassSpectrometry, Elsevier, New York, N.Y. (1990)]. The Fellgett advantageafforded by these techniques can also be realized by injecting ionpackets into the IM drift cell or TOFMS drift tube faster than thesequential (i.e., pulse-and-wait) duty cycle. Although both techniquesachieve separation based on time dispersion of the analytes,multiplexing of IMS or TOFMS have only been described as distinctlyseparate experiments.

For example, Hill and coworkers have demonstrated a 1.4-fold increase inIM sensitivity by in-phase frequency sweeping of ion gates(Bradbury-Nielsen design [N. E. Brabury and R. A. Nielsen, AbsoluteValues of the Electron Mobility in Hydrogen, Phys. Rev. 49, 388-393(1936)]) at the entrance and exit of the drift cell. The ion mobilityarrival time distributions were reconstructed from the frequency-domaininterferogram by application of a Fourier transform [F. J. Knorr, R. L.Eatherton, W. F. Siems, and H. H. Hill Jr., Fourier Transform IonMobility Spectrometry, Anal. Chem. 57, 402-406 (1985); R. L. Eatherton,W. F. Siems, and H. H. Hill Jr., Fourier Transform Ion MobilitySpectrometry of Barbiturates After Capillary Gas Chromatography, J. HighRes. Chrom. Chrom. Commun. 9, 44-48 (1986); R. H. St. Louis, W. F.Siems, and H. H. Hill Jr., Apodization Functions in Fourier TransformIon Mobility Spectrometry, Anal. Chem. 64, 171-177 (1992); Y.-H. Chen,W. F. Siems, and H. H. Hill Jr., Fourier Transform Electrospray IonMobility Spectrometry, Anal. Chim. Acta 334, 75-84 (1996); U.S. Pat. No.4,633,083 to Knorr, et al.]. Franzen later described fast-FT and fast-HTmultiplexing of IM by modulating the ion beam admittance to the driftcell by means of a Bradbury-Nielsen gate [U.S. Pat. No. 5,719,392 toFranzen]. A unique means for performing FT-IMS was also described byTarver and Siems, whereby a frequency-domain spectrum is obtained byeither frequency-sweeping a Bradbury-Nielsen gate and/orfrequency-sweeping the detector signal using a fast commutator [U.S.Pat. No. 6,580,068 to Tarver, et al.]. In these different multiplexedIMS experiments it is taught that, by means of their implementation, theduty cycle is only optimally increased to approximately 50%.

Knorr has also described Fourier transform-TOFMS [U.S. Pat. No.4,707,602 to Knorr]. The FT-TOFMS was equipped with an electron impactionization source and provided a 25-fold increase in sensitivity overconventional signal-averaging [F. J. Knorr, M. Ajami, and D. A.Chatfield, Fourier Transform Time-of-Flight Mass Spectrometry, Anal.Chem. 58, 690-694 (1986)]. Zare and coworkers have described Hadamardtransform-TOFMS to improve the instrumental duty cycle to nearly 50% byusing a modulated continuous ESI ion beam with an 8191-order Hadamardmatrix [A. Brock, N. Rodriguez, and R. N. Zare, Hadamard TransformTime-of-Flight Mass Spectrometry, Anal. Chem. 70, 3735-3741 (1998); A.Brock, N. Rodriguez, and R. N. Zare, Characterization of a HadamardTransform Time-of-Flight Mass Spectrometer, Rev. Sci. Inst. 71,1306-1318 (2000); F. M. Fernandez, J. M. Vadillo, J. R. Kimmel, M.Wetterhall, K. Markides, N. Rodriguez, and R. N. Zare, HadamardTransform Time-of-Flight Mass Spectrometry: A High-Speed Detector forCapillary-Format Separations, Anal. Chem. 74, 1611-1617 (2002); R. N.Zare, F. M. Fernandez, and J. R. Kimmel, Hadamard TransformTime-of-Flight Mass Spectrometry: More Signal, More of the Time, Angew.Chem. Int. Ed. 42, 30-35 (2003); U.S. Pat. No. 6,300,626 to Brock, etal.]. Zare and colleagues have suggested the possibility of attainingca. 100% duty cycle by electrostatic steering to modulate and direct theion beam to different regions of a position sensitive detector [R. N.Zare, F. M. Fernandez, and J. R. Kimmel, Hadamard TransformTime-of-Flight Mass Spectrometry: More Signal, More of the Time, Angew.Chem. Int. Ed. 42, 30-35 (2003).]. Independently, Dowell suggestedmodulating the ion beam by switching between two sources, or byalternatively modulating a single beam by electrostatic steering andutilizing two detectors [U.S. Pat. No. 5,331,158 to Dowell]. Note thatsteering modulation in TOFMS dates back to 1948 [A. E. Cameron and D. F.Eggers Jr., Ion “Velocitron,” Rev. Sci. Instrum. 19, 605-607 (1948)],but theoretical and practical implementation was not described until theearly 1970s by Bakker [J. M. B. Bakker, A Beam-Modulated Time-of-FlightMass Spectrometer Part I: Theoretical Considerations, J. Phys. E: Sci.Instrum. 6, 785-789 (1973); J. M. B. Bakker, A Beam-ModulatedTime-of-Flight Mass Spectrometer Part II: Experimental Work, J. Phys. E:Sci. Instrum. 7, 364-368 (1974).]. In contrast to FT and HT modes ofmultiplexing TOFMS, Myerholtz and colleagues have described a techniquebased on bunching and overlapping ion packets in the field-free driftregion and demodulating the resultant signal by using correlationalgorithms to improve TOFMS duty cycle to ca. 50% [U.S. Pat. No.5,396,065 to Myerholtz, et al.].

The present invention differs from the one-dimensional prior art (i.e.,IMS or TOFMS) in that significant gains in sensitivity, throughput, andS/N are obtained by two-dimensions of time dispersive analyte ionseparation, i.e., by coupling ion mobility-TOFMS and operating bothdispersive dimensions in a multiplex data acquisition mode describedherein.

BRIEF SUMMARY OF THE INVENTION

This invention describes a method for multiplexed data acquisition forgas-phase ion mobility coupled with mass spectrometry. The followingbrief summary more readily describes embodiments of the invention.

In one aspect of the present invention, there is a method for theacquisition of analytical data for a sample comprising the steps ofgenerating packets of gas-phase ions and neutral species from thesample; introducing the packets into a time dispersive ion mobilitydrift cell at a rate faster than the transient rate of separation of theions by the drift cell; separating the ions in a first dimensionaccording to their ion mobility; sampling the ions eluted by the ionmobility drift cell into a mass spectrometer; separating the ions in asecond dimension in the mass spectrometer; detecting a massspectrometric signal for the ions; and, processing the massspectrometric signal using the ion packet injection frequency and an ionmobility-mass-to-charge correlation function. Preferably, the step ofgenerating comprises generating packets of gas-phase ions and neutralspecies using a source selected from the group consisting of laserdesorption/ionization, electrospray, desorption electrospray ionization,nanospray, ion spray, photoionization, multiphoton ionization, resonanceionization, thermal ionization, surface ionization, electric fieldionization, chemical ionization, atmospheric pressure chemicalionization, radioactive ionization, discharge arc/spark ionization,laser induced breakdown ionization, inductively coupled plasmaionization, direct current plasma ionization, capacitively coupledplasma ionization, glow discharge ionization, microwave plasmaionization, and any combination thereof. Where laserdesorption/ionization is used, it may be one or more of atmosphericpressure MALDI, ultraviolet MALDI, infrared MALDI, direct LDI, surfaceenhanced laser/desorption ionization, and any combination thereof. Insome embodiments, the step of generating packets of gas-phase ions andneutral species comprises generating packets of gas-phase ions andneutral species from spatially distinct regions of a surface that isselected from the group consisting of steel, gold, silver, copper,glass, polymers, silicon, self-assembled monolayers, nitrocellulose,condensed-phase substrates, chemically functional moieties, chemicallyreactive moieties, biomolecules, and any combination thereof. Whenbiomolecules are analyzed, the biomolecules may be selected from thegroup consisting of proteins, nucleic acids, arrays thereof, patternsthereof, and layers thereof. In some embodiments, the polymers areselected from the group consisting of poly(dimethylsiloxane),elastomers, plastics, and teflon. Preferably, the step of separatingions in a first dimension comprises separating ions in an electric fieldselected from the group consisting of uniform electrostatic fields,periodic-focusing electrostatic fields, non-uniform electrostaticfields, traveling wave electrostatic fields, radiofrequencyelectrostatic fields, and any combination thereof. In some embodiments,the step of separating ions in a first dimension comprises separatingions by time dispersion on the basis of ion mobility, the ion mobilityselected from the group consisting of low-field mobility, high-fieldmobility, and any combination thereof. Preferably, the step ofseparating ions in a first dimension comprises separating ions bycollisions with one or more gases. In embodiments wherein the step ofseparating ions in a first dimension comprises separating ions bycollisions with one or more gases, preferably the one or more gases isselected from the group consisting of helium, neon, argon, krypton,xenon, nitrogen, oxygen, methane, carbon dioxide, water, methanol,methyl fluoride, ammonia, deuterated analogs thereof, tritiated analogsthereof, and any combination thereof. In embodiments wherein the step ofseparating ions in a first dimension comprises separating ions bycollisions with one or more gases, the collisions are preferablyselected from the group consisting of reactive collisions, non-reactivecollisions, and any combination thereof. In some embodiments, the stepof separating the ions in a second dimension comprises separating theions using a method selected from the group consisting of time-of-flightmass spectrometry, magnetic-sector mass spectrometry,electrostatic-sector mass spectrometry, double-focusing sector-fieldmass spectrometry, quadrupole mass spectrometry, ion trap massspectrometry, ion cyclotron resonance mass spectrometry, acceleratormass spectrometry, orbitrap mass spectrometry, and any combinationthereof. In some embodiments, the ions are further encoded in the seconddimension using multiplex frequency-domain analysis techniques orweighing design techniques or both; and, decoded by application of aFourier transform or Hadamard transform or both. In some embodiments,the step of introducing comprises introducing a plurality of packets ata plurality of energies. In some embodiments, the packets are introducedinto the ion mobility drift cell under varying conditions, with thevarying conditions comprising different experimental parameters forseparation and wherein one or more of the ion packets are encoded by thefrequency of introduction of the one or more ion packets. In someembodiments wherein the packets are introduced into the ion mobilitydrift cell under varying conditions comprising different experimentalparameters, preferably the experimental parameters are selected from thegroup consisting of drift cell voltage, drift cell gas pressure,temperature, identity of drift cell gases, and any combination thereof.In some embodiments, the ions comprise ions of single atoms and ions ofmolecules. Typically wherein ions of molecules are analyzed, themolecules are selected from the group consisting of molecules possessinga molecular weight less than 500 amu; molecules possessing a molecularweight less than 10,000 amu; molecules possessing a molecular weightless than 100,000 amu; molecules possessing a molecular weight greaterthan 100,000 amu; and, any combination thereof. In some embodiments, themethod further comprises forming a plurality of beams of gaseous ionsand neutral species from the packets, and wherein the step ofintroducing comprises introducing the plurality of beams into aplurality of ion mobility drift tubes to form a plurality ofmobility-separated beams. In some embodiments, the method furthercomprises introducing the plurality of mobility-separated beams into aplurality of CID (collision-induced dissociation) tubes. In someembodiments, the method further comprises introducing the plurality ofmobility-separated beams through at least one RF ion guide. In someembodiments, the method further comprises introducing the plurality ofmobility-separated beams into at least one mass spectrometer.Preferably, the mass spectrometer is a TOFMS. Preferably, the TOFMScomprises a position sensitive detector. In some embodiments, the methodfurther comprises the steps of segregating the mass spectrometric signalcorresponding to the output of a ion mobility channel. The plurality ofbeams may be formed from a single region on the sample, or may be formedfrom a plurality of regions on the sample. In some embodiments, themethod further comprises ionizing the gas phase neutral species.

In another aspect of the present invention, there is a method for theacquisition of analytical data for a sample comprising the steps ofgenerating packets of gas-phase ions and neutral species from saidsample; introducing said packets into a time dispersive ion mobilitydrift cell at a rate faster than the transient rate of separation ofsaid ions by said drift cell; separating said ions in a first dimensionaccording to their ion mobility; activating the ions as they elute fromthe ion mobility drift cell for dissociation into fragment ions;sampling the ions eluted by the ion mobility drift cell into a massspectrometer; separating said ions in a second dimension in said massspectrometer; detecting a mass spectrometric signal for the ions; and,processing said mass spectrometric signal using the ion packet injectionfrequency and an ion mobility-mass-to-charge correlation function.Preferably, the step of generating comprises generating packets ofgas-phase ions and neutral species using a source selected from thegroup consisting of laser desorption/ionization, electrospray,desorption electrospray ionization, nanospray, ion spray,photoionization, multiphoton ionization, resonance ionization, thermalionization, surface ionization, electric field ionization, chemicalionization, atmospheric pressure chemical ionization, radioactiveionization, discharge arc/spark ionization, laser induced breakdownionization, inductively coupled plasma ionization, direct current plasmaionization, capacitively coupled plasma ionization, glow dischargeionization, microwave plasma ionization, and any combination thereof.Where laser desorption/ionization is used, it may be one or more ofatmospheric pressure MALDI, ultraviolet MALDI, infrared MALDI, directLDI, surface enhanced laser/desorption ionization, and any combinationthereof. In some embodiments, the step of generating comprisesgenerating packets of gas-phase ions and neutral species from spatiallydistinct regions of a surface that is selected from the group consistingof steel, gold, silver, copper, glass, polymers, silicon, self-assembledmonolayers, nitrocellulose, condensed-phase substrates, chemicallyfunctional moieties, chemically reactive moieties, biomolecules, and anycombination thereof. When biomolecules are analyzed, the biomoleculesmay be selected from the group consisting of proteins, nucleic acids,arrays thereof, patterns thereof, and layers thereof. In someembodiments, the polymers are selected from the group consisting ofpoly(dimethylsiloxane), elastomers, plastics, teflon, and anycombination thereof. Preferably, the step of separating ions in a firstdimension comprises separating ions in an electric field selected fromthe group consisting of uniform electrostatic fields, periodic-focusingelectrostatic fields, non-uniform electrostatic fields, traveling waveelectrostatic fields, radiofrequency electrostatic fields, and anycombination thereof. In some embodiments, the step of separating ions ina first dimension comprises separating ions by time dispersion on thebasis of ion mobility, said ion mobility selected from the groupconsisting of low-field mobility, high-field mobility, and combinationsthereof. Preferably, the step of separating ions in a first dimensioncomprises separating ions by collisions with one or more gases. Inembodiments wherein the step of separating ions in a first dimensioncomprises separating ions by collisions with one or more gases,preferably the one or more gases is selected from the group consistingof helium, neon, argon, krypton, xenon, nitrogen, oxygen, methane,carbon dioxide, water, methanol, methyl fluoride, ammonia, deuteratedanalogs thereof, tritiated analogs thereof, and any combination thereof.In embodiments wherein the step of separating ions in a first dimensioncomprises separating ions by collisions with one or more gases, thecollisions are selected from the group consisting of reactivecollisions, non-reactive collisions, and any combination thereof. Insome embodiments, the step of activating ions occurs prior to said stepof separating said ions in said temporally-resolved mass spectrometer.In some embodiments, the step of activating ions as they elute from theion mobility drift cell for dissociation into fragment ions comprisesthe use of a technique selected from the group consisting of collisioninduced dissociation, surface induced dissociation, photodissociation,multiphoton dissociation, resonance enhanced multiphoton dissociation,blackbody induced radiative dissociation, electron capture dissociation,electron transfer dissociation, and any combination thereof. In someembodiments, the step of separating said ions in a second dimensioncomprises separating said ions using a method selected from the groupconsisting of time-of-flight mass spectrometry, magnetic-sector massspectrometry, electrostatic-sector mass spectrometry, double-focusingsector-field mass spectrometry, quadrupole mass spectrometry, ion trapmass spectrometry, ion cyclotron resonance mass spectrometry,accelerator mass spectrometry, orbitrap mass spectrometry, and anycombination thereof. In some embodiments, the ions are further encodedin the second dimension using multiplex frequency-domain analysistechniques or weighing design techniques or both; and, decoded byapplication of a Fourier transform or Hadamard transform or both.Preferably, the step of introducing comprises introducing a plurality ofpackets at a plurality of energies. In some embodiments, multiple ionpackets are introduced into the ion mobility drift cell under varyingconditions, the varying conditions comprising different experimentalparameters for separation and wherein one or more of said ion packetsare encoded by the frequency of introduction of said one or more ionpackets. In some embodiments wherein multiple ion packets are introducedinto the ion mobility drift cell under varying conditions comprisingdifferent experimental parameters for separation, the experimentalparameters are preferably selected from the group consisting of driftcell voltage, drift cell gas pressure, and any combination thereof. Insome embodiments, the ions comprise ions of single atoms and ions ofmolecules. In some embodiments, the molecules are selected from thegroup consisting of molecules possessing a molecular weight less than500 amu; molecules possessing a molecular weight less than 10,000 amu;molecules possessing a molecular weight less than 100,000 amu; moleculespossessing a molecular weight greater than 100,000 amu; and, anycombination thereof. In some embodiments, the method further comprisesforming a plurality of beams of gaseous ions and neutral species fromsaid packets, and wherein said step of introducing comprises introducingsaid plurality of beams into a plurality of ion mobility drift tubes toform a plurality of mobility-separated beams. In some embodiments, themethod further comprises introducing the plurality of mobility-separatedbeams into a plurality of CID tubes. In some embodiments, the methodfurther comprises introducing the plurality of mobility-separated beamsthrough at least one RF ion guide. In some embodiments, the methodfurther comprises introducing the plurality of mobility-separated beamsinto at least one mass spectrometer. Preferably, the mass spectrometeris a TOFMS. Preferably, the TOFMS comprises a position sensitivedetector. In some embodiments, the method further comprises the step ofsegregating the mass spectrometric signal corresponding to the output ofeach ion mobility channel. The plurality of beams may be formed from asingle region on the sample, or may be formed from a plurality ofregions on the sample. In some embodiments, the method further comprisesionizing the gas phase neutral species.

In another aspect of the present invention, there is an apparatus forion mobility-mass spectrometry comprising an ion source for generatingions; an ion mobility drift cell fluidly coupled to the ion source andreceiving ions from the ion source; a first timing controller coupled tothe ion source; a second timing controller coupled to the ion source; atemporally-resolving mass spectrometer fluidly coupled to the ionmobility drift cell, the mass spectrometer receiving ions from the ionmobility drift cell; and, a processor in communication with the ionsource, the ion mobility drift cell, the first timing controller, thesecond timing controller, and the mass spectrometer. In someembodiments, the second timing controller is a burst-mode timingcontroller. In some embodiments, the ion source comprises an ion sourceselected from the group consisting of atmospheric pressure MALDI,ultraviolet MALDI, infrared MALDI, direct LDI, surface enhanced laserdesorption/ionization, electrospray, desorption electrospray ionization,nanospray, ion spray, photoionization, multiphoton ionization, resonanceionization, thermal ionization, surface ionization, electric fieldionization, chemical ionization, atmospheric pressure chemicalionization, radioactive ionization, discharge arc/spark ionization,laser induced breakdown ionization, inductively coupled plasmaionization, direct current plasma ionization, capacitively coupledplasma ionization, glow discharge ionization, microwave plasmaionization, and any combination thereof. In some embodiments, the ionmobility drift cell produces an electric field selected from the groupconsisting of uniform electrostatic fields, periodic-focusingelectrostatic fields, non-uniform electrostatic fields, traveling waveelectrostatic fields, radiofrequency electrostatic fields, andcombinations thereof. In some embodiments, the ion mobility drift cellutilizes low-field mobility, high-field mobility, and any combinationthereof. In some embodiments, the mass spectrometer is selected from thegroup consisting of a time-of-flight mass spectrometer, amagnetic-sector mass spectrometer, an electrostatic-sector massspectrometer, a double-focusing sector-field mass spectrometer, aquadrupole mass spectrometer, an ion trap mass spectrometer, an ioncyclotron resonance mass spectrometer, an accelerator mass spectrometer,an orbitrap mass spectrometer, and any combination thereof.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated that the conception and specific embodimentdisclosed may be readily utilized as a basis for modifying or designingother structures for carrying out the same purposes of the presentinvention. It should also be realized that such equivalent constructionsdo not depart from the invention as set forth in the appended claims.The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages will be better understood from thefollowing description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings.

FIG. 1 is a schematic diagram of an ion mobility-time-of-flight massspectrometer;

FIG. 2 is (A) A two dimensional-plot of arrival time distribution vs.mass-to-charge. (B) A plot of arrival time distribution integrated overall mass-to-charge space. (C) A plot of mass-to-charge integrated overall arrival time distribution space. (D) A plot of mass-to-chargeintegrated over the arrival time distribution range of 1300 to 1400 μs;

FIG. 3 is a schematic diagram of the preferred embodiment of theinvention using an ion mobility-time-of-flight mass spectrometer;

FIG. 4. (A) A diagram illustrating the typical timing sequence inIM-TOFMS, (B) a diagram illustrating a timing sequence representing 100%duty cycle, and (C) a diagram illustrating the preferred embodiment ofthe invention by injecting ions into the ion mobility chamber at a ratefaster than the arrival time distribution.

FIG. 5A. (i) A diagram illustrating the ion injection timing, (ii) adiagram illustrating the arrival time distribution in the ion mobilitydimension for five hypothetical analyte peaks, and (iii) atwo-dimensional plot of the arrival time distribution further separatedby mass-to-charge for five hypothetical analytes.

FIG. 5B. (i) A diagram illustrating the ion injection timing, (ii) adiagram illustrating the arrival time distribution in the ion mobilitydimension for five hypothetical analyte peaks, and (iii) atwo-dimensional plot of the arrival time distribution further separatedby mass-to-charge for five hypothetical analytes in the preferredembodiment of the present invention.

FIG. 6. Diagrams illustrating timing sequences for different modes ofcorrelated data acquisition by IM-TOFMS. (A) Ion injection with constantrelative ion injection energies. (B) Ion injection with alternatingrelative ion injection energies. (C) Ion injection by cycling ofdifferent relative ion injection energies.

FIG. 7. (A) A two dimensional-plot of arrival time distribution vs.mass-to-charge using multiplex-mode ion injections (scheme (B) of FIG.6) in the analysis of three peptides (angiotensin III (RVYIHPF,M.W.=930.52), angiotensin II (DRVYIHPF, M.W.=1045.54), and angiotensin I(DRVYIHPFHL, M. W.=1295.69). (B) A plot of arrival time distributionintegrated over all mass-to-charge space. (C) A plot of mass-to-chargeintegrated over all arrival time distribution space. Guidelines 310 inthe two-dimensional plot are to assist in visualizing the arrival timedistribution-mass-to-charge correlation from each ion injection.

FIG. 8. Arrival time distributions for the data in FIG. 7 integratedover multiple ion injections. (A) The arrival time distribution obtainedfor the first ion injection (300, relatively high energy). (B) Thearrival time distribution obtained by integrating the nine subsequention injections (301, relatively low energy). (C) The arrival timedistribution obtained by integrating all ion injection events. Arrivaltime distribution plots (A) and (B) are offset for clarity.

FIG. 9. (A) A two dimensional-plot of arrival time distribution vs.mass-to-charge using multiplex-mode ion injections (scheme (B) of FIG.6) in the analysis of a tryptic digest of cytochrome c (horse heart).(B) A plot of arrival time distribution integrated over allmass-to-charge space. (C) A plot of mass-to-charge integrated over allarrival time distribution space; guidelines 330 in the two-dimensionalplot are to assist in visualizing the arrival timedistribution-mass-to-charge correlation from each ion injection.

FIG. 10. (A) A plot of mass-to-charge integrated over all arrival timedistribution space for the region of m/z 600-1200 for the data in FIG.9. (B) The arrival time distribution obtained by integrating over them/z region in (A).

FIG. 11. (A) Post-processing scheme for deconvolution of the ionmobility arrival time distribution using a multiplex-mode with constantrelative ion injection energies (e.g., see FIG. 6(A)). (B)Post-processing scheme for deconvolution of the ion mobility arrivaltime distribution using a multiplex-mode with alternating or cyclingrelative ion injection energies (e.g., see FIGS. 6B and 6C).

FIG. 12. A two-dimensional plot of arrival time distribution vs.mass-to-charge for analytes of different molecular classes (peptide,oligonucleotide, and carbon clusters). Guidelines 353-355 in thetwo-dimensional plot are to assist in visualizing the arrival timedistribution-mass-to-charge correlation for each class. (B) A plot ofarrival time distribution integrated over all mass-to-charge space. (C)A plot of mass-to-charge integrated over all arrival time distributionspace.

FIG. 13A. A hypothetical two-dimensional plot of the arrival timedistribution vs. mass-to-charge for analytes of three differentmolecular classes or one molecular class consisting of three differentcharge-states.

FIG. 13B. A hypothetical two-dimensional plot of the arrival timedistribution vs. mass-to-charge for analytes of three differentmolecular classes or one molecular class consisting of three differentcharge-states using multiplex-mode ion injection.

FIG. 14. (A) A two-dimensional plot of arrival time distribution vs.mass-to-charge for surface induced dissociation of four peptides afterthe ion mobility drift chamber and prior to mass spectrometry. (B) Aplot of arrival time distribution integrated over all mass-to-chargespace. (C) A plot of mass-to-charge integrated over all arrival timedistribution space. (D) A plot of mass-to-charge integrated over betweenthe two lines designated by arrows in (A).

FIG. 15A. A hypothetical two-dimensional plot of the arrival timedistribution vs. mass-to-charge for ion mobility followed by ionactivation/dissociation prior to mass analysis.

FIG. 15B. A hypothetical two-dimensional plot of the arrival timedistribution vs. mass-to-charge for ion mobility followed by ionactivation/dissociation prior to mass analysis using multiplex-mode ioninjection of the preferred embodiment.

FIG. 16. (A) Post-processing scheme for deconvolution of the ionmobility arrival time distribution using multiplex-mode ion injectionfor the analysis of multiple molecular classes or ion charge-states(e.g., see FIG. 13(B)). (B) Post-processing scheme for deconvolution ofthe ion mobility arrival time distribution using multiplex-mode ioninjection for ion mobility followed by ion activation/dissociation priorto mass analysis (e.g., see FIG. 15B).

DETAILED DESCRIPTION OF THE INVENTION

As used herein, “a” or “an” is defined herein as one or more. Unlessotherwise indicated or apparent by the context, the singular includesthe plural and the plural includes the singular herein.

As used herein, IM means ion mobility; MS means mass spectrometry whenused in the context of a method and MS means mass spectrometer when usedin the context of an apparatus; TOF means time-of-flight; TOFMS meanstime-of-flight mass spectrometry when used in the context of a methodand TOFMS means time-of-flight mass spectrometer when used in thecontext of an apparatus.

As used herein, “mobility tube” is an ion mobility cell; the terms ionmobility cell and mobility tube are synonymous herein.

As used herein “collision induced dissociation tube” or “CID tube” is atube in which high electric fields may be created sufficient to providecollision-induced dissociation of ions. In the present invention, theCID tube, when present can be used for collision-induced dissociation oralternatively, the collision-induced dissociation mode may be disabledand the CID tube may be used for cooling such as gas cooling and/or RFcooling.

Generally, an IM-TOFMS comprises generating packets of gas-phase ionsfrom said sample, introducing the ion packets into a time dispersive ionmobility drift cell, separating the ions according to their ionmobility, sampling the ions eluted by the ion mobility drift cell into atemporally-resolving mass spectrometer, further separating said ions insaid temporally-resolving mass spectrometer, and detecting a massspectrometric signal for the ions. Preferably the separation axes of theion mobility drift cell and that of the mass spectrometer areorthogonal.

Ion generation may be performed from any surface and from spatiallydistinct regions of a surface. These include, but are not limited to,surfaces of steel, gold, silver, copper, glass, polymers, self-assembledmonolayers, nitrocellulose, condensed-phase substrates, chemicallyfunctional moieties, chemically reactive moieties, biologically activespecies, oligonucleotide arrays, protein arrays, aptamer arrays,antibody arrays, patterns and layers thereof, and any combinationthereof. The polymers may be any polymers, with some non-limitingexamples including poly(dimethylsiloxane), elastomers, plastics, teflon,and any combination thereof.

The first separation dimension in these methods is that of ion mobility.A variety of electric fields, known to those of skill in the art, may beused for this purpose. Electric fields used in this separation may be ofany type, including, but not limited to, uniform electrostatic fields,periodic-focusing electrostatic fields, non-uniform electrostaticfields, traveling wave electrostatic fields, radiofrequencyelectrostatic fields, and any combination thereof. The ion mobilitytechniques used may be low-field mobility, high-field mobility, and anycombination thereof. Drift tube gases used in this separation may be ofany type, including, but not limited to, helium, neon, argon, krypton,xenon, nitrogen, oxygen, methane, carbon dioxide, water, methanol,methyl fluoride, ammonia, deuterated analogs thereof, tritiated analogsthereof, and any combination thereof. The drift tube gases aid in theseparation by colliding with the species in the drift tube. Thesecollisions may be reactive collisions, non-reactive collisions, and anycombination thereof. The drift tube may have one or more gases.

The second separation dimension in these methods is that of massspectrometry. The mass spectrometric technique employed in this regardmay be any such technique, including, but not limited to, time-of-flightmass spectrometry, magnetic-sector mass spectrometry,electrostatic-sector mass spectrometry, double-focusing sector-fieldmass spectrometry, quadrupole mass spectrometry, ion trap massspectrometry, ion cyclotron resonance mass spectrometry, acceleratormass spectrometry, orbitrap mass spectrometry, and any combinationthereof.

An illustration of the major components of an ionmobility-time-of-flight mass spectrometer (IM-TOFMS) 1 is presented inFIG. 1. An IM-TOFMS instrument consists of five main components: asource of ions 10, an ion mobility drift chamber 20, a region after thedrift chamber for collimating and focusing the ions eluting from thedrift chamber 40, a time-of-flight mass spectrometer 50, and a computer52 and associated electronics 51, 76, 77 for controlling the instrument.

Biological ions may be generated in the source by matrix assisted laserdesorption/ionization (MALDI), electrospray (ESI), or nanospray. For oneskilled in the art, it is clearly recognized that any means forgenerating ions proximal to the opening orifice 11 of the drift chamber20 could be used. These include, but are not limited to, atmosphericpressure MALDI, ultraviolet MALDI, infrared MALDI, direct LDI (laserdesorption ionization), surface enhanced laser desorption/ionization,electrospray, nanospray, ion spray, photoionization, multiphotonionization, resonance ionization, thermal ionization, surfaceionization, electric field ionization, chemical ionization, atmosphericpressure chemical ionization, radioactive ionization, dischargearc/spark ionization, laser induced breakdown ionization, inductivelycoupled plasma ionization, direct current plasma ionization,capacitively coupled plasma ionization, glow discharge ionization,microwave plasma ionization, and any combination thereof. The ion sourceregion can further be operated at reduced pressure (<760 Torr) or atelevated pressure (>760 Torr) with means for transporting the ions fromtheir point of inception to the plane of the drift chamber opening 11. Atiming controller 51 provides a means for injecting ions into the driftchamber in a time-controlled manner. This is necessary to define t₀ inthe ion mobility arrival time distribution and to for the mass spectrum[U.S. Pat. No. 6,683,299 to Fuhrer, et al.]. Timing-control of the ionbeam is accomplished by using an intrinsically pulsed-source of ions asproduced by MALDI, or by modulating a continuous ion beam (e.g., ESI)for admittance vs. no-admittance into the drift chamber, for example, bymeans of a mechanical chopper or electrostatic gate 21. Alternatively, ameans for storing ions and injecting them in discrete intervals such aswith a pulsed ion funnel [T. Wyttenbach, P. R. Kemper, and M. T. Bowers,Design of a New Electrospray Ion Mobility Mass Spectrometer, Int. J.Mass Spectrom. 212, 13-23 (2001)] or a pulsed ion trap (U.S. Pat. No.6,559,441 to Clemmer) can be used.

The drift chamber 20 consists of a housing 22 in which the pressure canbe accurately controlled by a metered drift gas supply 23 which deliversdrift gas to the drift chamber proximal to the exit of the chamber 24 orthe entrance of the chamber 25. Inside of the drift chamber housing 22,there consists a plurality of conductive elements 26 which are linked toone another by a series of resistive elements (not shown). Byapplication of a potential from a voltage supply 28 via 29, theplurality of conductive elements 26 serves to generate anelectric-field. In the prior art the electric-field thus formed isuniform across the longitudinal axis 70 of the drift chamber. It isrecognized that alternate geometries of the conductive elements, ornon-uniform valued resistive elements, can be utilized for generatingnon-uniform fields (U.S. Pat. No. 6,639,213 to Gillig, et al.). Thedrift chamber is terminated in an exit plane defined by anelectrostatically controlled ion gate 31, or an exit orifice 32, fortransmitting the ions eluting from the drift chamber to an ion opticsregion 40.

The ion optics region 40 is used for collimating and focusing the ionseluting from the drift chamber 20 by means of electrostatic or magneticfield ion optical elements 41. Those skilled in the art recognize thatthese elements can consist of a variety of geometries or combinationsthereof for the purposes of ion beam collimation and focusing. Thisregion can be further delineated by an exit aperture for purposes ofcreating a conductance limit and by reducing the gas number density bymeans of vacuum pumping 43. The ion beam is then transmitted in thisconditioned state to the source 61 of a time-of-flight mass spectrometer50. The TOFMS source consists of a series of electrostaticallyaddressable plates and grids 62 (which comprise the source 61) fordefining t₀ of the time-of-flight measurement. Potentials are applied tothese plates and grids by means of voltage supplies 53 via connections54. It is recognized by those skilled in the art that the number,spacing, potential, and specific time-domain waveform applied to theplates and grids can be varied for purposes of increasing iontransmission and/or time resolution in the time-of-flight measurement.Further, it is recognized that the orientation of the TOF source 61relative to the longitudinal-axis of ion beam propagation 70 from thedrift chamber can be varied. The orientation illustrated in the FIG. 1is an orthogonal-time-of-flight 50, although a linear-time-of-flightcould be used. In the orthogonal arrangement, ions are accelerated outof the TOF source into a field-free drift region 72, perpendicular (ornearly so) to the axis of their drift chamber translation 70. In theinstrument of FIG. 1, the TOF drift region is capped by a reflectron 73for purposes of kinetic energy focusing of the ion packet prior tostriking electron multiplier multichannel plate 74 whereby the electroncascade is collected at the anode of the detector. Voltage supply 55 isconnected to the multiplier multichannel plate 74; voltage supplies 57are connected to the reflectron 73. This signal is transmitted via 75 toan amplifier 76 and subsequently to a time-to-digital converter 77 andcomputer 52 where it is registered and stored for processing. For oneskilled in the art, it is recognized that other means for ion detectionsuch as continuous dynode electron multipliers, Daly-type detectors,etc., can also be used with alternate means for collecting, storing, andprocessing the ion signal thus obtained.

An example of the two-dimensional data obtained by using IM-TOFMS isillustrated in FIG. 2 for the peptides obtained from a proteolyticdigest (tryptic) of bovine hemoglobin. The arrival time distribution(FIG. 2, left) is the signal that would be registered if the detectorwere placed at the exit plane of the drift chamber 32, that is,monitoring the one-dimensional ion mobility separation based primarilyon the charge to collision cross-section of the ion. The arrival timedistribution typically spans 0.1 to several 10 s of ms depending on theparticular experimental arrangement. In contrast, the mass spectrometerdisperses and detects the eluting ions over a duration of ca. 10-100 μs.Owing to the short timescale of the mass spectrometer analysis relativeto that of the ion mobility, many mass spectra can be obtained over thecourse of the arrival time distribution to yield a two-dimensional plotlike that shown in FIG. 2 (center). The resolution in the arrival timedistribution can be improved by using interleaving data acquisition bymeans of post-processing or by using position sensitive detection (U.S.Pat. No. 6,683,299 to Fuhrer, et al.). By integrating the mass spectralsignals over all arrival time distribution space, one obtains anintegrated mass spectrum as illustrated in the bottom panel of FIG. 2.This is what would be obtained by performing mass spectrometry in theabsence of ion mobility. However, by first dispersing the peptidesignals (e.g., 100-105) by ion mobility, mass spectral congestion can besignificantly reduced in the analysis of complex mixtures. The top panelin FIG. 2 illustrates the integrated mass spectrum obtained acrossarrival times of 1300-1400 μs (i.e., centered about the peptide signal103 (VGGHAAEYGAEALER, residues 17-31 of the bovine hemoglobinα-subunit)). Signals occurring outside this range are eliminated, i.e.,chemical noise is significantly attenuated.

Also illustrated in FIG. 2 is that the ion signals arising for thismixture of peptides align in the two-dimensional spectrum in a highlypredictable manner whereby ion signals for higher m/z analyte ionstypically elute from the drift chamber at longer times than smaller m/zanalyte ions. This is illustrated by the guideline 106, which isincluded to assist in visualizing this trend, which is hereafter termeda trendline. The trendline for a particular class of analytes (e.g.,peptides) is a correlation function ƒ(t) relating the arrival timedistribution to the m/z of an ion under particular ion mobilityconditions. It is also apparent that greater than ca. 90% of thetwo-dimensional space does not, and is not expected to, contain analytesignals (i.e., regions above-left and below-right of the trendline 106),which ultimately represents inefficient sampling.

This inefficiency and its consequences are addressed by the presentinvention. In the present invention, as illustrated in FIG. 3, aseparate timing controller 80 is a burst mode timing controller and istriggered by the ion injection pulse of the prior art via 51. Thissecond controller 80 is used to trigger a plurality of ion injectionpulses for each sampling trigger (i.e., t₀). For example, FIG. 4Aillustrates using MALDI at a repetition rate of 30 Hz (i.e., ioninjection events 150 separated by 33.3 ms). The arrival timedistribution for the peptides of a tryptic digest of horse heartcytochrome c 155, illustrate that the separation of these peptides iscomplete in ca. 500 μs. Other numerical indicators used in FIG. 3 arethe same as those used in FIG. 1. In the FIG. 4A this represents aninstrumental duty cycle of ca. 1.5%. The duty cycle approaches 100% whenthe time between ion injection events approaches the temporal extent ofthe arrival time distribution. For the purposes of this description, ioninjection at a rate slower than or equal to the slowest elutingcomponent will hereafter be termed sequential duty cycle. Ion injectionat a rate faster than the slowest eluting component (i.e., timecorrelation for separate injection events is not apparent in onedimension, but rather frequency encoded) is hereafter termed multiplexedduty cycle. In embodiments of the present invention, packets of ions areintroduced into a time dispersive ion mobility drift cell at a ratefaster than the transient rate of ion packet separation. The concepts ofsequential and multiplex duty cycle are illustrated in FIGS. 4B and 4C,respectively. FIG. 4B shows arrival time distributions of cytochrome c(simulated based on 155) where ion injection 150 is performed at a rateof 2 kHz (i.e., ion injection every 500 μs). Because this ion injectionrate is commensurate with the duration of the arrival time distributionfrom the drift chamber, it represents essentially 100% sequential dutycycle. FIG. 4C illustrates the preferred embodiment of the inventionwhereby ion injection is performed at a rate faster than 100% sequentialduty cycle for the drift chamber, i.e., 10 kHz in FIG. 4C. In thissituation, the arrival time distributions are no longer discrete, whichmeans that they cannot be simply summed or averaged as in the case ofFIG. 4A or 4B. Rather, the signals for individual ion injections arephase-shifted dependent upon the ion mobility of the particular analyte.Owing to this phase-shift, the convoluted arrival time distribution 158must be decoded/demodulated to recover the IM time correlation. In thepreferred embodiment, the arrival time distribution is demodulated bymeans of a mass spectrometer. In some embodiments of present invention,the mass spectrometric signal is processed using the ion packetinjection frequency and an ion mobility-mass-to-charge correlationfunction.

Along these lines multiple ion packets can be introduced into the ionmobility drift cell under varying conditions. These varying conditionsmay be different experimental parameters for separation. In this way,one or more of the ion packets are encoded by their frequency ofintroduction. Examples of such experimental parameters include, but arenot limited to, drift cell voltage, drift cell gas pressure,temperature, identity of drift cell gases, and any combination thereof.

FIG. 5 illustrates demodulation of the convoluted arrival timedistribution. The analysis of a hypothetical five component 170-174analyte mixture by using conventional IM-MS means is shown in FIG. 5A.In the analysis time domain (i), the single ion injection 175 producesan arrival time distribution 176 as shown in (ii), where signals fallalong a trendline 177 (with correlation function ƒ(t)) when subsequentlysampled by mass spectrometry (iii). Again, note the large regionsabove-left and below-right of the trendline 177 which do not containanalyte signals. In the present invention, this sampling space is filledwith analyte signal by operation in a multiplex-mode of ion injection.This is illustrated in FIG. 5B, where the initial ion injection 175 isfollowed thereafter with a series of 10 additional injections 180. Thisyields a plurality of ion packets in the drift chamber at the same time,but at different stages of ion separation (ii). When the convolutedarrival time distribution 182 is subsequently sampled by the massspectrometer, the two-dimensional separation (iii) yields 11 trendlines185 each offset from one another by Δt, which equals the temporalspacing between ion injections 180.

In this example, the arrival time distribution for separating theanalytes of one ion packet/injection is ca. 1 ms. By injecting 10additional ion packets each separated by 100 μs, the arrival timedistribution dimension must be increased by a factor of 2 to fullyaccommodate the phase-shifted separations. However, there is a netfactor of 5.5 increase in total ion signal detected when normalized tothe total analysis time (i.e., 11 trendlines/2 times increase insampling space). Ultimately, this signal intensity enhancement islimited by the highest multiplex-mode frequency that can be demodulatedby the mass spectrometer (provided the total number of ions injected perpulse remain constant as a function of frequency). This frequency isdetermined by four complementary factors for the particular instrumentalarrangement and conditions utilized: (i) resolution in the ion mobilitydimension, (ii) resolution in the mass spectrometry dimension, (iii)time of elution for the lowest mobility analyte, and (iv) slope of thetrendline. Typical values for the instrumentation presently used rangefrom 20 to 100 for ion mobility resolution (t/Δt, full width at halfmaximum (FWHM)), 100 to 10,000 for TOFMS resolution (t/2Δt, FWHM), and0.2 to 10 ms for the elution time of the lowest mobility analytes. Thus,examining two practical extremes, i.e., high mobility resolution(t/Δt=100)/short elution time (0.2 ms) and low mobility resolution(t/Δt=20)/long elution time (10 ms), yields a multiplex frequency upperlimit in the range of 2 to 500 kHz (500 to 2 μs pulse separation). Theselimits are provided for illustrative purposes and future improvements inboth instrumentation and separations would provide an even broader rangeof values. It should be noted that by using MALDI in the presentembodiment, the pulse width of the ion injection at high multiplexfrequency is not detrimental to IM resolution as it is defined by thelaser pulse width (0.5 to 15 ns) which is a factor of ca. 10³ to 10⁶faster than the multiplex-mode frequency limits outlined above.

In addition to varying the period of the multiplex-mode frequency 252(FIG. 6), the relative ion injection energy of the pulse train 250 canalso be varied at a second or additional frequencies to affect thenumber and types of ions injected. For example, FIG. 6A illustrates aconstant relative ion energy multiplex-mode at a frequency of 10 kHz251. In FIG. 6B, superimposed on the multiplex-mode frequency 255 is a 1kHz injection frequency 254 of higher ion injection energy. By changingthe relative ion injection energy (e.g., FIG. 6B) one can promote higherenergy processes (e.g., in-source decay) at one frequency 254 and retainlower energy ionization conditions 255 at a second frequency. By usingthis approach, several spectra are obtained at different experimentalconditions (e.g., 257-259 FIG. 6C), but in the same rapid multiplex-modeanalysis.

A demonstration of a preferred embodiment is illustrated in FIG. 7 for amixture of 3 peptides: human angiotensin III 306 (RVYIHPF, M.W.=930.52),human angiotensin II 307 (DRVYIHPF, M.W.=1045.54), and human angiotensinI 308 (DRVYIHPFHL, M.W.=1295.69). MALDI was performed usingα-cyano-4-hydroxycinnamic acid (CHCA, M.W.=189.16) giving rise to theadditional matrix-derived signals of [CHCA+H]⁺ 304 and to [2CHCA+H]⁺305. In this analysis, the sampling cycle timing was initiated at afrequency of 150 Hz, whereby the first MALDI event 300 was performed athigh relative energy (ca. 14.8 μJ pulse⁻¹) and 9 subsequent MALDI events301 were performed at lower relative energy (ca. 9.1 μJ pulse⁻¹) at afrequency of 2000 Hz (500 μs ion injection separation). This isanalogous to the timing scheme depicted in FIG. 6B. For each ioninjection event, trendlines 310 are illustrated to assist in visualizingthe data. The convoluted arrival time distribution is shown in FIG. 7Band the integrated mass spectrum (over all injections) is shown in FIG.7C. The lower energy MALDI pulses 301 result in lower ion yields 303than that at higher MALDI energies 302; however, the former providessofter ionization conditions, which reduces spectral complexity. Forexample, FIG. 8 illustrates the arrival time distributions obtained byintegrating over the different energy multiplex-mode signals. FIG. 8Ashows the expanded arrival time distribution of the higher energy pulse302. In addition to peaks for the matrix 304,305 and protonatedmolecular peptide ions 306-308, several additional features are noted314, which correspond to in-source decay fragment ions. These fragmentions are not observed by integrating the nine lower energy ion injectionarrival time distributions 303 as illustrated in FIG. 7B. Further, theion mobility resolution appears to be slightly improved over the higherMALDI energy ion injection (e.g., inspection of signals 306 and 307 inFIGS. 8A and B). Integrating signals for both high and low energyregimes provides enhanced sensitivity as shown in FIG. 8C. Thus, bymodulating the relative energy for ionization/injection, particular ionspecies produced by different energy regimes can be selectively acquiredin the same analysis.

FIG. 9 illustrates data for the multiplex-mode analysis of a trypticdigest of cytochrome c. The three analyte signals of highest abundancecorrespond to: the heme porphyrin group 326 (C₃₄H₃₀O₄N₄Fe, M.W.=616.18),TGPNLHGLFGR 327 (fragment 28-38, M.W.=1168.33), and CAQCHTVEK+heme 328(fragment 14-22 including covalently attached heme (at positions ¹⁴Cysand ¹⁷Cys), M.W.=1634.36). MALDI was again performed using CHCA givingrise to the characteristic matrix-related signals 324 [CHCA+H]⁺ and 325[2CHCA+H]⁺. The sampling cycle timing was initiated at a frequency of150 Hz, whereby the first MALDI event 320 was performed at high relativeenergy (ca. 14.8 μJ pulse⁻¹) and 2 subsequent MALDI events 321 wereperformed at lower relative energy (ca. 9.1 μJ pulse⁻¹) at a frequencyof 2000 Hz. For each ion injection event, trendlines 330 are indicatedto assist in visualizing the data. Inspection of the integrated arrivaltime distributions for high 322 and low 323 relative energy ioninjection events reveals significant differences in the relativeabundance observed for the small molecule heme group 326, peptide 327,and peptide+ligand (heme) 328.

To illustrate the differences in ion signals observed at both high andlower energy, FIG. 10 focuses on the region including heme 326,TGPNLHGLFGR 327, CAQCHTVEK+heme 328. The integrated mass spectrum forthe mass range of m/z=600 to 1700 is presented in FIG. 10A, Theintegrated arrival time distribution for this mass range inmultiplex-mode operation is illustrated in FIG. 10B. The wavelength usedfor MALDI in this analysis (349 nm, frequency-tripled Nd:YLF)corresponds closely with a resonant line in the Soret region of heme [G.Loew, Structure, Spectra, and Function of Heme Sites, Int. J. QuantumChem. 77, 54-70 (2000)]. Thus, at higher ion injection energy, therelative abundance of heme 326 is significantly higher relative to lowerion injection energy, which better favors ionization and injection ofintact peptide molecules (e.g., 327). For example, the abundance ratioof heme-to-peptide (326/327) is 1.57 and 0.41 for high energy and lowenergy injections, respectively. In contrast, the abundance ratio ofpeptide+heme-to-peptide (328/327) remains nearly constant regardless ofinjection energy (0.31 and 0.40 for high and low energies,respectively). This observation suggests that the small molecule-peptidecomplex exhibits ionization characteristics that resemble those for thepeptide rather than the small molecule alone. By utilizing differentenergy regimes in the same multiplex-mode analysis, individual spectrarepresenting these different ionization/injection conditions can beobtained nearly simultaneously.

A schematic flowchart for processing of the multiplex data is presentedin FIG. 11. In general, the correlated raw data is examined with the apriori knowledge of the multiplex-mode frequency (v, Δt) and the numberof ion injections (m) (FIG. 11A). By selecting two or more points in asingle trendline, the correlation function (ƒ(t)) can be readilydefined. Note that for a given gas number density (N) and electric fieldstrength (E), ƒ(t) must only be determined once, because the slope ofƒ(t) does not vary considerably for a particular molecular class.Resolution in the arrival time distribution can be used as a convergencevariable to ensure an appropriate estimate of ƒ(t) was made. Thedeconvoluted spectrum (c_(ff)) for equal energy ion injections (seee.g., FIG. 6(A)) is then obtained by:

${{c_{ff}\left( {n\;\Delta\; t} \right)} = {{\sum\limits_{n = 0}^{m}\;{f\mspace{11mu}(t)\mspace{11mu} f\mspace{11mu}\left( {t + {n\;\Delta\; t}} \right)\mspace{34mu} n}} = 0}},1,{2\ldots\mspace{11mu} m}$

which sums the signals from each individual trendline. When two or moreion injection energies or multiplex frequencies (e.g., ν′, Δt₁ and ν″,Δt₂) are used (see e.g., FIG. 6B), the deconvoluted spectra are obtainedby:

$\begin{matrix}{{{c_{ff}\left( {n\;\Delta\; t_{1}} \right)} = {{\sum\limits_{n = 0}^{m}\;{f\mspace{11mu}(t)\mspace{11mu} f\mspace{11mu}\left( {t + {n\;\Delta\; t_{1}}} \right)\mspace{101mu} n}} = 0}},1,{2\ldots\mspace{11mu} m}} \\{{{c_{ff2}\left( {n\;\Delta\; t_{2}} \right)} = {{\sum\limits_{n = 0}^{m}\;{f\mspace{11mu}\left( {t + {\Delta\; t_{2}}} \right)\mspace{11mu} f\mspace{11mu}\left( {t + {n\;\Delta\; t_{2}}} \right)\mspace{40mu} n}} = 0}},1,{2\ldots\mspace{11mu} m}}\end{matrix}$

which is illustrated schematically in FIG. 11 (B). Note that thisprocessing scheme readily scales with additional multiplex frequencies(i.e., >2).

In the analysis of complex materials (e.g., biological samples), IM-MScan easily distinguish between molecules of different molecular class.For example, FIG. 12 illustrates the separation of peptides 356-357,oligonucleotides 358-362, and carbon clusters derived from C₆₀ 364 andC₇₀ 363 (the latter are used as both mobility and m/z internalstandards). Each of these molecular classes exhibits a differenttrendline (353, 354, 355 for peptides, oligonucleotides, and carbonclusters, respectively) owing to the characteristic packing efficiencyof particular molecular classes (e.g., carbonclusters>oligonucleotides>peptides>lipids etc.) [J. M. Koomen, B. T.Ruotolo, K. J. Gillig, J. A. McLean, D. H. Russell, M. Kang, K. R.Dunbar, K. Fuhrer, M. Gonin, and J. A. Schultz, Oligonucleotide Analysiswith MALDI-Ion Mobility-TOFMS, Anal. Bioanal. Chem. 373, 612-617(2002)]. The resulting multiple trendlines 353-355 are analogous to thesituation when modulating an ESI ion source coupled with IM-MS, wherebymultiple trendlines are observed that arise from generating analyte ionshaving multiple charge states [see e.g., C. S. Hoaglund-Hyzer, A. E.Counterman, and D. E. Clemmer, Anhydrous Protein Ions, Chem. Rev. 99,3037-3079 (1999), and references therein].

Consider the hypothetical situation of multiple trendlines depicted inFIG. 13A. As noted above these trendlines 373-375 can arise fromdifferent molecular classes in MALDI (which predominantly producessingly charged ions below ca. m/z 5000), or different charge states inmodulated ESI (e.g., 373=3⁺, 374=2⁺, and 375=1⁺ ion signals). By using amultiplex-mode of data acquisition as described herein, there is notheoretical limitation to the number of trendlines that can besimultaneously analyzed, except for the degenerate case of two analyteson different trendlines having the exact same m/z. In the latter casethe situation would be quickly apparent (as severely degraded arrivaltime distribution resolution after deconvolution) and can be correctedmathematically. The multiplex-mode operation in the analysis of multipletrendlines is depicted in FIG. 13B. Owing to the conserved nature ofƒ(t) for a given N, E, and molecular class, the different trendlines373-375 are defined by the first ion injection event which serves as aframe of reference for all subsequent multiplex ion injections. Notethat a priori knowledge of the number/types of analyte(s) is notnecessary for accurate decoding of the modulated signals.

Contemporary IM-MS can also be operated in an IM-MS/MS mode, which hasparallels with conventional tandem MS/MS techniques for parent andfragment ion analysis. In IM-MS/MS operation, the IM dimension providesseparation of the parent ions (similar to MS¹). If the ions are thenactivated and dissociate prior to their sampling in the MS dimension(MS²), then both parent ion and fragment ion spectra are obtained nearlysimultaneously [D. E. Clemmer in U.S. Pat. No. 6,559,441; Schultz et al,in U.S. Pat. No. 6,683,299 and pending U.S. application Ser. Nos.10/689,173, 10/967,715, and 10/969,643]. Importantly, if both the parentand the fragment ions arrive in the source of the MS at the same time,they will both be correlated to the same arrival time in the IMdimension. This is illustrated in FIG. 14, which shows both the parention trendline 379 and the fragment ion trendlines 380-383 for[des-Arg₉]-bradykinin 375, bradykinin 376, gramicidin s 377, andsubstance p 378, respectively. The parent ion trendline 379 is whatwould be observed in the absence of post-IM ion activation. In theexample of FIG. 14, the parent ions are impinged onto a fluorinated-selfassembled monolayer surface for dissociation as they elute from the IMdrift cell, but prior to entering the source of the MS. Guideline 379 inthe two-dimensional plot is to assist in visualizing the arrival timedistribution-mass-to-charge correlation for the parent ions andguidelines 380-383 for visualizing the fragment ions.

An IM-MS/MS experiment is schematically illustrated in FIG. 15A. In thisexample, the parent ions 390-394 exhibit a characteristic trendline 395.As these ions elute from the IM drift cell they are activated (e.g.,photo-fragmented) and dissociate prior to entering the source of the MS,so that their characteristic fragment ions 396 are arrival timecorrelated on fragment ion trendlines 397-401. By virtue of the parentions being separated along the correlation function ƒ(t) 395, thefragment ion trendlines are offset from one another in arrival time Δt(402-405). In essence, almost all parent species are activated fornearly simultaneous dissociation and analysis, which in itself providesa Fellgett multiplex advantage. This is in stark contrast withcontemporary MS/MS techniques whereby typically a single parent analyteis selected for fragmentation, or at best a small subset of parent ionsare selected for simultaneous fragmentation (U.S. Pat. No. 4,978,852 toWilliams, et al). One skilled in the art should recognize that virtuallyany means for activating the parent ions for dissociation can be used.These include, but are not limited to collision induced dissociation,surface induced dissociation, photodissociation, multiphotondissociation, resonance enhanced multiphoton dissociation, blackbodyinduced radiative dissociation, electron capture dissociation, electrontransfer dissociation, and combinations thereof. For literature exampleof some of these methods of activation, please see the following;collision induced dissociation [C. S. Hoaglund-Hyzer, J. Li, and D. E.Clemmer, Mobility Labeling for Parallel CID of Ion Mixtures, Anal. Chem.72, 2737-2740 (2000)], surface induced dissociation [E. G. Stone, K. J.Gillig, B. T. Ruotolo, and David H. Russell, Optimization of aMatrix-Assisted Laser Desorption Ionization-Ion Mobility-Surface InducedDissociation-Orthogonal-Time-of-Flight Mass Spectrometer: SimultaneousAcquisition of Multiple Correlated MS1 and MS2 Spectra, Int. J. MassSpectrom. 212, 519-533 (2001); E. G. Stone, K. J. Gillig, B. T. Ruotolo,K. Fuhrer, M. Gonin, J. A. Schultz, and D. H. Russell, Surface-InducedDissociation on a MALDI-Ion Mobility-Orthogonal Time-of-Flight MassSpectrometer: Sequencing Peptides from an “In-Solution” Protein Digest,Anal. Chem. 73, 2233-2238 (2001)], or photodissociation [J. A. McLean,K. J. Gillig, B. T. Ruotolo, M. Ugarov, H. Bensaoula, T. Egan, J. A.Schultz, and D. H. Russell, Ion Mobility-Photodissociation (213nm)-Time-of-Flight Mass Spectrometry for Simultaneous Peptide MassMapping and Peptide Sequencing, Proceedings of the 52nd American Societyfor Mass Spectrometry Conference, Montreal, Canada, June (2003) on atimescale such that dissociation occurs prior to entering the source ofthe MS can be used. As new ion activation techniques emerge, we envisionthat they too could be interfaced for application in IM-MS/MS.

The correlated multiplex-mode of operation described herein is equallywell suited for application in IM-MS/MS as illustrated in FIG. 15B. Bydetermining the sequential Δt offsets 402-405 in the arrival timedistribution for each correlated fragment ion trendline, bothmultiplex-mode parent ion spectra and multiplex-mode fragment ionspectra can be deconvoluted/decoded. From inspection of FIG. 15B, itappears that if an arrival time offset Δt (e.g., 404) is nearly the sameas the time separation Δt of subsequent multiplex-mode ion injections,that fragment ions derived from multiple parent ion species (e.g.,analytes 392 and 393) will exhibit nearly overlapping fragment iontrendlines and parent ion/fragment ion correlation could be lost.However, analogous to the case of multiple trendlines exhibitingdifferent slopes for ƒ(t) (e.g., FIG. 13B) a frame of reference for thesignals arising from fragment ions of a particular parent ion arereadily defined by the first ion injection event. Indeed, although morechallenging, it is also possible to readily demodulate/decodemultiplex-mode spectra containing both multiple trendlines for molecularclasses (or analyte charge-states, e.g., FIG. 13(B)) and their fragmention correlated trendlines (e.g., FIG. 15B) in IM-MS/MS experiments.

A schematic flowchart for the processing of multiplex-mode spectracontaining multiple trendlines is illustrated in FIG. 16A. In the caseof multiple classes of ions, or charge states of analyte (e.g., FIG.13B), the correlated raw data can be deconvoluted by defining a uniquecorrelation function (e.g., ƒ(t), g(t), h(t) . . . etc.) for eachtrendline in the spectra. Along with the multiplex frequency and numberof injections, each trendline correlation function can be refined againusing known arrival time resolution as the convergence variable. Asimilar post-processing scheme for the analysis of IM-MS/MSmultiplex-mode data is presented in FIG. 16B. However, in this case, anew set of correlation functions must be defined for each fragmention/parent ion correlation. Iteration using the parent ion trendlinecorrelation function ƒ(t), fragment ion correlation functions, and themultiplex frequency can be performed until the arrival time resolutionconvergence tolerance is met.

The present invention provides a means for multiplex-mode dataacquisition by multiplexing ion injection into the first time dispersivedimension (i.e., IM) and demodulating the mobility phase-shifted signalsby means of an ion mobility-m/z correlation determined in two-dimensions(i.e., IM-MS). In conjunction with this correlated multiplex-mode, onecan realize further enhancements in signal acquisition rate by FT or HTmultiplexing of the mass spectrometer dimension. In the post-processingschemes outlined in FIGS. 11 and 16, demodulation of the FT- or HT-MSsignal would first be performed by application of a Fourier or Hadamardtransform and followed by determination of the IM-MS correlationfunction. In this manner of operation, effectively two multiplex-modesof data acquisition would be performed simultaneously, i.e., one in theIM dimension and the second in the MS dimension. By using bothmultiplexing modes in tandem, signal enhancements (or throughput) of 10³to 10⁶ can be achieved. For example, one may encode ions in the seconddimension using multiplex frequency-domain analysis techniques orweighing design techniques or both and decode by application of aFourier transform or Hadamard transform or both.

Additional dimensions of liquid- or gas-phase separations (e.g.capillary electrophoresis, capillary electrochromatography, highperformance liquid chromatography, gas chromatography, etc.) can be usedin a multiplexed-mode coupled with the multiplexed-mode IM-MS describedherein.

The present method can be used to analyze ions of single atoms and/ormolecular ions. The molecular ions may have any molecular weight,including ions of molecules possessing a molecular weight less than 500amu, ions of molecules possessing a molecular weight less than 10,000amu, ions of molecules possessing a molecular weight less than 100,000amu, ions of molecules possessing a molecular weight greater than100,000 amu, and any combination thereof.

Also within the scope of the present invention is an apparatus for ionmobility-mass spectrometry having an ion source for generating ions, anion mobility drift cell fluidly coupled to the ion source and receivingions from the ion source, a first timing controller coupled to the ionsource, a second timing controller coupled to the ion source, atemporally-resolving mass spectrometer fluidly coupled to the ionmobility drift cell, the mass spectrometer receiving ions from the ionmobility drift cell, and a processor in communication with the ionsource, the ion mobility drift cell, the first timing controller, thesecond timing controller, and the mass spectrometer. In preferredembodiments, the second timing controller is a burst-mode timingcontroller. The ion source can be any ion source, including, but notlimited to the following ions sources: atmospheric pressure MALDI,ultraviolet MALDI, infrared MALDI, direct LDI, surface enhanced laserdesorption/ionization, electrospray, nanospray, ion spray,photoionization, multiphoton ionization, resonance ionization, thermalionization, surface ionization, electric field ionization, chemicalionization, atmospheric pressure chemical ionization, radioactiveionization, discharge arc/spark ionization, laser induced breakdownionization, inductively coupled plasma ionization, direct current plasmaionization, capacitively coupled plasma ionization, glow dischargeionization, microwave plasma ionization, and any combination thereof.The ion mobility drift cell may use uniform electrostatic fields,periodic-focusing electrostatic fields, non-uniform electrostaticfields, traveling wave electrostatic fields, radiofrequencyelectrostatic fields, and combinations thereof. It may also use otherfields. The ion mobility drift cell may utilize low-field mobility,high-field mobility, and any combination thereof. Examples of the massspectrometer include, but are not limited to, a time-of-flight massspectrometer, a magnetic-sector mass spectrometer, anelectrostatic-sector mass spectrometer, a double-focusing sector-fieldmass spectrometer, a quadrupole mass spectrometer, an ion trap massspectrometer, an ion cyclotron resonance mass spectrometer, anaccelerator mass spectrometer, an orbitrap mass spectrometer, and anycombination thereof.

The invention has application also to parallel processing of multipleion signals which have been discretely input into multiple ionmobility/mass spectrometers. Recently, several patents and applicationshave described instruments wherein ions from one or more discreteionization sources can be uniquely focused into each ion mobilitychannel within a specially constructed array of ion mobility channels(see U.S. Pat. No. 6,897,437; pending U.S. application Ser. No.10/969,643, filed Oct. 20, 2004, both are incorporated by reference asthough fully described herein), and furthermore, that the output of eachion mobility channel in such an ion array of ion mobility channels canbe separately focused into its own region of a position sensitivedetector within a mass spectrometer (see pending U.S. application No.60/685,247, filed May 27, 2005; U.S. application No. 60/685,240, filedMay 27, 2005; U.S. application Ser. No. 10/689,173, filed Oct. 20, 2003;U.S. application Ser. No. 10/967,715, filed Oct. 18, 2004 and U.S. Pat.No. 6,683,299, issued Jan. 27, 2004, all of which are incorporated byreference as though fully described herein). In this way, one maycorrelate the mass spectrometric signal corresponding to the output ofeach ion mobility channel. The present invention can be used in suchcases to increase the ion throughput of each of the individual channelswithin the array of ion mobility and mass detection channels (providedby the discrete mobility tubes each feeding ions through the massspectrometer to either discrete ion detectors or discrete regions of aposition sensitive ion detector within the mass spectrometer). Anexample of this would be when multiple laser beams are focused intomultiple locations on a surface from which ions are desorbed. Ions fromeach discrete location are focused into their own single, discrete ionmobility channel within a multiple channel ion mobility spectrometerwhich is itself fluidly connected to a position sensitive massspectrometer. Each of the resulting mobility and mass spectra can thenbe unambiguously correlated with a specific location on the sample. Byusing the teachings of the present invention applied to each individuallaser beam, each individual mobility channel, and each individual massspectrometer channel within the array, the overall throughput of thetotal spectrometer can be increased. Other non-exhaustive examples wouldinclude parallel processing of the outputs of an array of ion traps, anarray of electrospray sources, or the output of a field emitter array.Ions within a spatially delocalized area or volume, which would includean elongated ion beam or from a delocalized plasma, could be partitionedinto each of the multiple ion mobility/mass channels so that each ionmobility and mass channel would be filled and processed according to theteachings of the present invention.

The present method can be used to analyze both ions and post-ionizedneutrals of single atoms and/or molecular ions (i.e., ionization of gasphase neutral molecules) by sequential application of two or moreionization techniques. A non limiting example would use a series ofsteps for creating and analyzing both the directly desorbed ions and thesubsequently post-ionized directly desorbed neutral species in the caseof direct laser desorption of ions and neutrals from a surface using amicrofocused laser or ion beam. The steps of the analysis would be 1)desorption of ions and neutrals by impinging, for example, amicro-focused laser or ion beam or beams onto one or more spots on thesurface; 2) extraction of the directly ejected ions into one or more ofthe ion mobility-mass spectrometry analysis channels 3) post-ionizationof the slowly evolving neutral gas plume after a fixed time delay whichmay be chosen from a range of several hundred nanoseconds to severalmicroseconds 4) repetition of steps 1, 2, and 3 at a rate which willgenerate desirable statistics and which will over-fill the individualion mobility-mass spectrometry channels, and 5) use of the deconvolutiontechniques described in the present invention so that two plots of ionmobility and mass can be reconstructed; one plot for the directlydesorbed ions and one plot for the subsequently post-ionized directlydesorbed neutrals. It is also clear that it may be desirable in certainapplications to analyze only desorbed ions or only post-ionized neutralspecies after deflecting the directly desorbed ions thus preventingtheir penetration into the ion mobility channels.

All patents and publications referenced herein are hereby incorporatedby reference. It will be understood that certain of the above-describedstructures, functions, and operations of the above-described embodimentsare not necessary to practice the present invention and are included inthe description simply for completeness of an exemplary embodiment orembodiments. In addition, it will be understood that specificstructures, functions, and operations set forth in the above-describedreferenced patents and publications can be practiced in conjunction withthe present invention, but they are not essential to its practice.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the invention asdefined by the appended claims. Moreover, the scope of the presentapplication is not intended to be limited to the particular embodimentsof the process, machine, manufacture, composition of matter, means,methods and steps described in the specification. As one will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized. Accordingly, the appended claims areintended to include within their scope such processes, machines,manufacture, compositions of matter, means, methods, or steps.

1. An apparatus for ion mobility-mass spectrometry comprising: a ionsource for generating gaseous ions and neutral species; an ion mobilitydrift cell fluidly coupled to said ion source and receiving ions fromsaid ion source; a first timing controller coupled to said ion source; asecond timing controller coupled to said ion source, said second timingcontroller is a burst-mode timing controller; a temporally-resolvingmass spectrometer fluidly coupled to said ion mobility drift cell, saidmass spectrometer receiving ions from said ion mobility drift cell; and,a processor in communication with said ion source, said ion mobilitydrift cell, said first timing controller, said second timing controller,and said mass spectrometer.
 2. The apparatus of claim 1, wherein saidion source is selected from the group consisting of laserdesorption/ionization, electrospray, desorption electrospray ionization,nanospray, ion spray, photoionization, multiphoton ionization, resonanceionization, thermal ionization, surface ionization, electric fieldionization, chemical ionization, atmospheric pressure chemicalionization, radioactive ionization, discharge arc/spark ionization,laser induced breakdown ionization, inductively coupled plasmaionization, direct current plasma ionization, capacitively coupledplasma ionization, glow discharge ionization, microwave plasmaionization, and any combination thereof.
 3. The apparatus of claim 2,wherein said laser desorption/ionization is selected from the groupconsisting of MALDI, direct LDI, surface enhanced laserdesorption/ionization, and any combination thereof.
 4. The apparatus ofclaim 1, wherein said ion mobility drift cell produces an electric fieldselected from the group consisting of uniform electrostatic fields,periodic-focusing electrostatic fields, non-uniform electrostaticfields, traveling wave electrostatic fields, radiofrequencyelectrostatic fields, and combinations thereof.
 5. The apparatus ofclaim 1, wherein said ion mobility drift cell utilizes low-fieldmobility, high-field mobility, and any combination thereof.
 6. Theapparatus of claim 1, wherein said mass spectrometer is selected fromthe group consisting of a time-of-flight mass spectrometer, amagnetic-sector mass spectrometer, an electrostatic-sector massspectrometer, a double-focusing sector-field mass spectrometer, aquadrupole mass spectrometer, an ion trap mass spectrometer, an ioncyclotron resonance mass spectrometer, an accelerator mass spectrometer,an orbitrap mass spectrometer, and any combination thereof.